A way to carry out earth drilling in a more developed manner compared to prior art, is formerly known e.g. from Finnish Patent No. 95618. The drilling head of the drilling unit of the drilling apparatus, being exploited in this connection, is formed as shown in FIG. 1 of a first frame part and a second frame part, in the drilling surfaces of which there has been arranged drilling organs, such as drill bits or like, of the first and second drilling means or in other words of the pilot and the reamer. In the solution in question the second organs of the flushing means for removal of drilling waste, being generated, are arranged to lead drilling waste by means of an assembly belonging to the counterpart surface arrangement, which connects the said drilling means together for a drilling situation unrotatively in respect with each other and in both directions longitudinally, which, in other words, is being carried out as an advantageous embodiment by loosening grooves, belonging to a bayonet coupling, placed longitudinally in the outer periphery of the first frame part.
The solution in question has got very good feedback from professionals in the art and a very big market share both domestically and abroad. The good success of the solution in question is based on the totally new construction in its time, which enables transmitting of flushing medium to the drilling surface and removing of same therefrom advantageously in a way that does not weaken other structures of the drilling apparatus in any way.
On the other hand particularly in sampling drilling, the meaning of undisturbed and homogeneous return flow of drilling waste, or of the sampling material to be collected, is considered very important. In this connection in those sampling drills usually being used before, there has been used a so called reverse flow or reverse circulation (RC-principle), in which connection on the principle being shown e.g. in FIG. 2, both feeding of the flushing medium and its return flow are led in a flow assembly, being placed at the center of the drilling device, from which flushing medium is being led furthermore in radial direction to the drilling surface and into which it is finally being returned by means of return flow assemblies, being placed in the radial direction at the drilling end of the drilling device. By leading the return flow in this way from the outer periphery of the bit to the return flow channel, placed at its center, it is possible to improve decisively the quality of sampling particularly in the above purpose.
The solution according to Finnish Patent No. 95618 is very efficient in practice, though particularly in those structures that are related to traditional sampling drilling, when the exhaust flow channel of drilling waste is formed according to traditional practice of the space between the center part of the drill and the casing part, the solution in question has led in certain situations to disproportionately large dimensions of the drill components, in order to enable high enough flow velocity of the return flow and as low as possible volume of flushing medium. The corresponding problem may be faced on other occasions as well, where components are being used in the drilling apparatus that have e.g. dimensions that deviate to some extent from those being standardized.